Disclaimer: I have only recently started driving on the motorway regularly
Surely whatever lane you're in, 70mph is an acceptable speed to be doing? I keep finding that when I'm in the fast lane (eg when overtaking cars in the middle lane) at 70mph, I find I have someone driving 2 metres behind me in a way that suggests they enjoy causing a pile up. Once I'm able to get back into the middle lane they will rush past at well over 70mph.
Did I miss the memo where the fast lane became part of the German Autobahn?